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Animal Form and Function ‐5‐Compartments for Body Fluids•fig. 40.4 clearly shows that multicellular animals have many cells that are bathed in watery solution, and of course all the cells contain a watery solution •a typical vertebrate has 3 fluid compartments...(see fig. 42.16 upper) 1.the fluid within cells...•contains most (~2/3) of the water in an animal’s body 2.the fluid that fills the spaces between cells...•exchanges nutrients and wastes with blood in capillaries •exchanges nutrients and wastes with intracellular fluid 3.the fluid surrounding blood cells... •together, interstitial fluid and plasma make up all the fluid outside of cells... •in animals with closed circulatory systems (vertebrates and some invertebrates)... •interstitial fluid and plasma are kept separate•but in many invertebrates those two fluids are effectively combined into a single fluid... fig. 42.16 (upper) Some fluid compartments and fluid h

Animal Form and Function ‐6‐Osmosis and Pressure Can Move Water Between Compartments•plasma membrane separates intracellular fluid from extracellular fluid... •recall that membranes are quite permeable to water•water can move between intracellular fluid and extracellular fluid by osmosis•review figs. 7.12 and 7.13 •recall that there are two unidirectional fluxes, but the net flux of water is in the direction toward the region with the highest solute concentration(toward the hypertonic solution) •recall as well that the permeability of a membrane to water is greatly enhanced by the presence of water channel proteins... •cells require a fairly stable internal environment in which to function... •the movement of water between compartments is important for that internal environment•variations in internal [salt], pH, cell volume and other variables are permissible within a given range •large changes may be detrimental to the cell or even result in cell death •recall the changes in cell volume and shape for red blood cells in different environments (see fig. 7.13) •in vertebrates and many invertebrates interstitial fluid and plasma are separated from each other by blood vessel walls... •the single layer of endothelial cells that make up a capillary (see previous fig. 42.16, upper) •the multiple layers of cells that make up veins and arteries, or venules and arterioles •pressure differencesare used to move fluid between these compartments...•e.g.blood pressure generated by contractions of cardiac musclecan force water and dissolved solutes betweenthe endothelial cells of a capillary •this pressure difference is used to deliver nutrients from blood plasma to interstitial fluid hypertonic environment membrane hypotonicenvironment hypotonic environment hypertonicenvironment

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Animal Form and Function ‐7‐THE ORGANIZATION OF ANIMAL BODIES•differentiated cellsarise during the development of an animal from a single-celled zygote... they

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